SQL Server

System.ObjectDisposedException: Cannot access a disposed object. Getting Linq to prepopulate/explicitly fetch data from the database.

Tim Huffam — Mon, 02 Jun 2008 21:41:57 GMT

Exception: System.ObjectDisposedException: Cannot access a disposed object.

Object name: 'DataContext accessed after Dispose.'.

This can occur when using Linq to SQL to retrieve data from a database - and when you try to access data after the data context object has been disposed. More specifically, the exception occurs when trying to access an item that has not yet been retrieved from the database and the data context object has been disposed.

This often occurs when using a variable, that was populated within a using(...datacontext) block, after the using() block. This works fine when accessing data explicitly retrieved within the using() block - but the exception occurs when you try to access other items that were not retrieved eg a related item such as a foreign key or child table.

To reproduce this error, comment out lines 6 and 9 in the sample code below. This will raise the exception on line 11.

We can be solve this by telling the data context to explicitly retrieve the items you'll need. This can be done a number of ways while the datacontext is still in scope.

Access the items directly eg with a linq expression eg something followed by .ToList(), .Single() or .First(). Line 9 does this in the sample below.
Use the DataLoadOptions class - this is a way of telling the datacontext what additional data to retrieve. Lines 4, 5 and 6 do this in the sample below (6 is commented out just while testing line 9).

* Note that you only need one of these - so either include lines 4-6 (all uncommented) or line 9.

The following code shows how to do both. This is based on a database using a table called Parent and a table called Child. The Child table has a ParentId field that is a foreign key to the Parent table. The DataClasses1DataContext was generated using Linq to SQL.

1. Parent outerParent;
2. using (var db = new DataClasses1DataContext())
3.  {
4.   DataLoadOptions dlo = new DataLoadOptions();
5.   dlo.LoadWith<Parent>(p => p.Childs);
6.   //db.LoadOptions = dlo;
7.   var outerParent = (from parent in db.Parents
8.                     select parent).First();
9.   List<Child> children = outerParent.Childs.ToList();
10. }
11. int i = outerParent.Childs.Count;

HTH

Tim

Cannot change column to Not Null: Cannot insert the value NULL into column '', table '.dbo.Tmp_'; column does not allow nulls.

Tim Huffam — Thu, 29 May 2008 09:05:03 GMT

When modifying a table SQL Server (2005) and unchecking a column's 'Allow Nulls' (ie trying to make the column Not Null) the following error may occur:

'<tablename>' table
- Unable to modify table.  
Cannot insert the value NULL into column '<columnname>', table '<dbname>.dbo.Tmp_<tablename>'; column does not allow nulls. INSERT fails.
The statement has been terminated.

This occurs if there is already data in this table and this column contains nulls.

The solution is to simply update the data in this table so that this column does not contain nulls then change the column to not null. eg if this column was of type int you could do this:

UPDATE [<dbname>].[dbo].[<tablename>]
SET [<integercolumnname] = -1

SQL Server 2005 error: VIA Provider: The specified module could not be found.

Tim Huffam — Wed, 12 Mar 2008 05:00:53 GMT

When trying to use sqlcmd.exe - and not specifying the server and instance name I got the following error:

C:\Program Files\Microsoft SQL Server\90\Tools\Binn>sqlcmd -E -d master
HResult 0x7E, Level 16, State 1
VIA Provider: The specified module could not be found.

Sqlcmd: Error: Microsoft SQL Native Client : An error has occurred while establi
shing a connection to the server. When connecting to SQL Server 2005, this failu
re may be caused by the fact that under the default settings SQL Server does not
 allow remote connections..
Sqlcmd: Error: Microsoft SQL Native Client : Login timeout expired.

The solution is to simply specify the server (and instance) name eg:

C:\Program Files\Microsoft SQL Server\90\Tools\Binn>sqlcmd -S localhost\SQLEXPRESS -E -d master

SQL Server - dropped table that was users default table - causes: Cannot Open User Default Database, Login Failed Microsoft SQL Server, Error 4064

Tim Huffam — Sun, 10 Feb 2008 12:59:58 GMT

This error (Cannot Open User Default Database, Login Failed Microsoft SQL Server, Error 4064), occurs when you try to connect to a SQL Server 2005 server where the default database for your user has been dropped. Unfortuntely this occurs in Microsoft SQL Server Studio too - which means you cannot use it to resolve the issue (ie change the default database assigned to your login).

However you can resolve this using ye-olde command prompt...

1) At the command prompt enter:

sqlcmd -E -d master

This command logs you onto the db server using specifying master as your default db.
2) Within the SQL command prompt enter:

alter login [MYDOMAIN\UserName] with default_database = master

This changes the default database setting against your login.

3) Then enter:
go

This executes the command.
4) Then enter:

quit

This quit's you out of the sqlcmd tool/prompt.

You screen will look something like:

C:\>sqlcmd -E -d master
1> alter login [MYDOMAIN\UserName] with default_database = master
2> go
3> quit

SQL Server datetime set blank or null = SQL Server error: System.Data.SqlTypes.SqlTypeException: SqlDateTime overflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM.

Tim Huffam — Wed, 08 Nov 2006 07:32:00 GMT

This error (System.Data.SqlTypes.SqlTypeException: SqlDateTime overflow. Must be between 1/1/1753 12:00:00 AM and 12/31/9999 11:59:59 PM.) will occur if you try to pass an uninitialised DateTime value into an SQL Server stored procedure from .NET code (in my case C# in an ASP.NET app).

To work around this you must pass in a value - null will not work.

In my case I have a generated class that passes a System.DateTime variable into the System.Data.SqlClient.SqlCommand.ExecuteNonQuery() method. So my only easy option was to make sure I pass in a valid DateTime value (I couldnt be shagged in altering my codesmith templates).

I decided to go with just setting the DateTime to a mimimum value (and just handling that in any code that had to look out unset dates) - however of you try to using System.DateTime.MinValue you'll be shit out of luck - as this equates to: 00:00:00.0000000, January 1, 0001 - which SQL Server does not support.

Instead set your DateTime variable to System.Data.SqlTypes.SqlDateTime.MinValue.Value - which equates to the lowest date value that a SQL Server datetime can store (01/01/1753 00:00).

Problem solved (for now) - this is the kind of hack that makes half-baked software possible ;-)

Update: 9/11 *** Special explanation note for those who didn't read or understand paragraph 3:

This is a workaround (read: "half-baked" or "hack") based on two constraints:

existing code that requires a valid System.DateTime value
a lack of time, motivation or it's a non-production crappy piece of half-baked software that'll never be used by anyone else but yourself.

However, if you are building a commercial/decent system that will be used and/or maintained by others, you *could* pass DBNull.Value to SQL Server (if you don't have a datetime value to pass) - however that would just be another hack (because if you dont have a value to pass, you'll potentially be overwriting an existing value with null) - so a proper, fully-baked solution, you should not be passing anything but instead change your db entry point to either provide an sproc or sql that only updates db columns as required (no shit Sherlock).

Cannot add diagram to SQL Server 2005 DB: Database diagram support objects cannot be installed because this database does not have a valid owner.

Tim Huffam — Wed, 05 Jul 2006 07:36:00 GMT

When trying to add a diagram to an SQL Server 2005 db I got the following error:

Database diagram support objects cannot be installed because this database does not have a valid owner. To continue, first use the Files page of the Database Properties dialog box or the ALTER AUTHORIZATION statement to set the database owner to a valid login, then add the database diagram support objects.

I tried the suggestion mentioned in the message but that didnt work. Also found that SQL Server Management Studio does not like you trying to change various permissions - it only works certain ways (go figure).

Anyway, eventually found this post with the solution (thanks very much to cutiepie) being:

In SQL Server Management Studio do the following:

Right Click on your database, choose properties
Goto the Options Page
In the Dropdown at right labeled "Compatibility Level" choose "SQL Server 2005(90)"

SQL Server 2005 SQLExpress error: ...provider: Named Pipes Provider, error 40 - Could not open connection to SQL Server

Tim Huffam — Sun, 29 Jan 2006 23:32:00 GMT

I got this error immediately after installing VS2005 & SQL Server 2005 Express and trying to establish my first connection using the new server - not a good start at all - and by the looks of it, it's happened to many hundreds, if not thousands, of others too.

Generally this error occurs if you cannot connect to the SQL server - as the message says (no sh*t). However, what's not obvious is why...

First suggestion is to make sure that you specifiy the instance name as well as the server name (christ knows why, but when MS refer to "Server Name" they really mean "Server Instance Name") eg if your server was named 'bigturnip' then you need to specify 'bigturnip\sqlexpress' (where sqlexpress is the instance name - this one just happens to be the default used by SQL Server 2005 SQLExpress).

If that doesn't help, then go into the SQL Server Configuration Manager and make sure you've enabled Named Pipes & TCP (if you're using it) and also go into the Surface Area Configuration tool and make sure you've set it for local &/or remote connection for the connection types you want to use. Then restart the SQL Server (instance) service.

HTH

Tim

Converting SQL Server data types to .NET types

Tim Huffam — Fri, 09 Dec 2005 23:32:00 GMT

The following link contains a list of Microsoft SQL Server data types and a list of their .NET CLR equivalents: http://msdn2.microsoft.com/en-us/library/ms131092.aspx

And this link shows the mapping between C# built-in types and the .NET CLR types: http://msdn2.microsoft.com/en-us/library/ya5y69ds.aspx

Great multi-vendor DB Tool == Aqua Data Studio

Tim Huffam — Thu, 24 Nov 2005 22:42:00 GMT

Came across a great multi-vendor db tool today called Aqua from AquaFold.

It's much like the Enterprise Manager that comes with MS SQL Server - but, personally I think it's waaaay better - more functionality (intelli-sense would be one of my favourites) etc.

It supports most of the main rdbms's:

Oracle
- 8i/9i/10g

DB2 UDB
- 7.x/8.x

MS SQL Server
- 2000/2005/7/MSDE

Sybase ASE
- 11.x/12.x/15

Sybase Anywhere
- 6/7/8/9

Informix (IDS)
- 7.x/9.4/10

Postgresql
- 7.x/8.0

MySQL
- 3.x/4.x/5

Generic JDBC[tm]

Generic ODBC

Syntax error converting from a character string to uniqueidentifier.

Tim Huffam — Tue, 04 Oct 2005 01:40:00 GMT

I got this error (Syntax error converting from a character string to uniqueidentifier.) when trying to run the following SQL insert from within Query Analyser:

insert into [dbo].[TeamUsers] ([TeamId], [UserId], [RoleType]) values (3, 'f7b681c0faeb11d69aed0008c7e6fa6a',2)

Column UserID is a uniqueidentifier.

So I tried it without the quotes:

insert into [dbo].[TeamUsers] ([TeamId], [UserId], [RoleType]) values (3, f7b681c0faeb11d69aed0008c7e6fa6a,2)

.. but got this error:

The name 'f7b681c0faeb11d69aed0008c7e6fa6a' is not permitted in this context. Only constants, expressions, or variables allowed here. Column names are not permitted.

The problem, however was not that I needed to convert it from a string or integer to a uniqueidentifier, but rather that I had used an incorrect format. Instead it should have looked like this (using the standard GUID format) - and be quoted:

insert into [dbo].[TeamUsers] ([TeamId], [UserId], [RoleType]) values (3, 'f7b681c0-faeb-11d6-9aed-0008c7e6fa6a',2)